UC Riverside

Emerging per- and polyfluoroalkyl substances (PFAS) have garnered significant attention as advancements in high-resolution mass spectrometry reveal novel PFAS in various environmental phases. These PFAS, with diverse functional groups, may serve as alternatives to legacy PFAS or byproducts of fluoropolymers. This dissertation investigates the biotransformation and defluorination of two types of emerging PFAS: chlorinated polyfluorocarboxylic acids (Cl-PFCAs) and fluoroalkylether substances (ether PFAS). It addresses knowledge gaps regarding their environmental fates and develops innovative treatments for bioremediation.First, the structure-biodegradability relationship of twelve ether PFCAs was examined in activated sludge communities. Polyfluorinated ethers with specific structural features, such as at least one –CH2– moiety adjacent to or a C=C bond near the ether bond, underwent biotransformation via oxidative and hydrolytic O-dealkylation under aerobic conditions. These reactions led to unstable fluoroalcohol intermediates that spontaneously defluorinate. This study also demonstrates how aerobic biotransformation can complement advanced reduction processes, offering cost-effective treatment strategies for recalcitrant ether PFAS like GenX. Second, the anaerobic biotransformation and defluorination of Cl-PFCAs were explored. Significant defluorination was achieved through anaerobic microbial communities via hydrolytic dechlorination, which was favored with increased chlorine substitutions. An enriched anaerobic culture dominated by Desulfovibrio aminophilus and Sporomusa sphaeroides demonstrated defluorination activity towards chlorotrifluoroethylene tetramer acid (CTFE4). The enhanced biodegradability due to Cl substitution highlights the potential for developing alternative polyfluoroalkyl substances that are more biodegradable and less toxic. Furthermore, the anaerobic biotransformation and defluorination of other ether PFAS were investigated, including chlorine-substituted and unsaturated ether PFAS. The study highlights cobalt's crucial role in biotransformation, with pure cultures of S. sphaeroides and D. aminophilus demonstrating distinct pathways. These findings suggest bioremediation strategies and the importance of designing ether PFAS with functional groups to enhance biodegradability. Finally, screening for biocatalysts involved in hydrolytic dechlorination revealed that the functional biocatalysts have molecular weights lower than 3000 Da and are not proteins, suggesting metal-related complexes might be the active biocatalysts. This dissertation provides essential insights into the environmental fate of emerging PFAS, the development of biodegradable alternatives, and the design of innovative, cost-effective biotechnologies for PFAS treatment, with significant implications for environmental management and sustainable industrial practices.